FIG. 6 shows a solar cell disclosed in Patent Literature 1. The conventional solar cell comprises a plurality of photoelectric conversion layers 13, the photoelectric conversion layer 13 having a solar cell element 11 and a lens L. The solar cell element 11 comprises a p-type GaAs buffer layer 13a, a p-type InGaP-BSF layer 13b, a p-type GaAs base layer 13c, an n-type GaAs emitter layer 13d, an n-type InGaP window layer 13e, and an antireflection layer 15. These layers 13a to 15 are stacked on a semiconductor substrate 12 in this order. The solar cell element 11 further comprises a separation grid 16 which separates the photoelectric conversion layer 13, a contact layer 14 around the detector side of the photoelectric conversion layer 13, a recoupling prevention layer 17 around the outer circumference of the contact layer 14, a detector side electrode 18 and a back side electrode 19.
Sunlight penetrates the lens L and the antireflection layer 15, and the n-type InGaP window layer 13e is irradiated with the sunlight. This irradiation of the sunlight generates electric power.
FIG. 7 shows a solar cell disclosed in Patent Literature 2. The conventional solar cell comprises a top cell 1 made of InGaP and a bottom cell 2 made of GaAs. The top cell 1 and the bottom cell 2 are joined electrically through a quantum tunneling layer 3. The top cell 1 absorbs light having a wavelength different from the wavelength of light absorbed by the bottom cell 2 so as to cause the solar cell to generate electric power efficiently.